The invention is generally directed to processes for the preparation of toner and developer compositions, and more specifically, the present invention is directed to the preparation of polymers by an aquabulk polymerization, that is heat transfer bulk polymerizations wherein surfactants and stabilizers are avoided. In one embodiment, the process of the present invention comprises adding water to a reaction vessel, heating the reaction vessel, subsequently adding to the reaction vessel a solution of monomers and initiator; heating the contents of the reaction vessel for an effective time period, followed by the removal of water; thereafter further heating to about the melt temperature of polymer, subsequently adding to the molten melt mixed polymer product pigments and optional additives such as charge control agents. The polymer product, such as styrene acrylates, styrene methacrylates, styrene butadienes, polyesters, and the like can be selected as a toner resin. In embodiments, the toner compositions can be comprised of the polymer products obtained with the processes of the present invention, pigment particles, and optional known additives, such as charge additives like quaternary ammonium hydrogen bisulfates, including distearyl methyl hydrogen ammonium bisulfate, distearyl dimethyl ammonium methyl sulfate and the like. Also, the aforementioned toner compositions usually contain pigment particles comprised of, for example, carbon black, like REGAL 330.RTM., magnetites, or mixtures thereof, cyan, magenta, yellow, blue, green, red, or brown components, or mixtures thereof thereby providing for the development and generation of black and/or colored images. The toner compositions of the present invention in embodiments thereof possess excellent admix characteristics, and maintain their triboelectric charging characteristics for an extended number of imaging cycles, exceeding for example 1,000,000 in a number of embodiments. The toner and developer compositions of the present invention can be selected for electrophotographic, especially xerographic imaging and printing processes, including color processes.
Certain suspension polymerization processes for the preparation of polymers are known, wherein there are suspended monomers in droplet form in a nonsolvent liquid thereof such as water, and adding thereto two types of suspending components, such as a protective colloid like ALKANOL.TM. a sulfonated surfactant, and a finely divided insoluble inorganic salt like tricalcium phosphate to minimize and stabilize the coalescence of the droplets. In suspension polymerization process, there is provided an aqueous phase comprising an aqueous mixture comprising water, monomers such as styrene monomer, butadiene monomer and the like, a suspension stabilizing agent, and a chain propagating amount of one or more free radical polymerization initiators, the ratio of the comonomer being, for example, between about 80:20 and about 95:5 by weight, the weight proportion of water to the combination of comonomers being between about 0.8:1 and about 2:1 and thereafter heating the aqueous phase to a temperature between about 50.degree. C. and about 130.degree. C. at a pressure between about 20 psi and about 140 psi when, for example, butadiene monomer is selected until at least about 90 percent by weight of the monomers are copolymerized to form an aqueous suspension of discrete copolymer particles. Examples of disadvantages associated with suspension polymerization include forming a suspension that entraps some of the stabilizer; and heating, for example, to 95.degree. C., and forming a styrene butadiene copolymer with an undesirable high ash content (TCP), that is for example the ash content is from about 0.04 percent to about 0.15 percent. With undesirable ash content there can result toners with polymers that exhibit undesirable admix characteristics. Also, without the surfactant the monomers oil droplets will eventually coalesce, and suspension failure will result.
In patentability search reports the following United States patents were listed: U.S. Pat. No. 4,528,321, which discloses a polymer dispersing system comprising a polymerization stabilizer and a nonionic compound, such as alkanols, polyalkylene glycol monoethers, alkonates, and benzyl alcohol, reference for example column 3; U.S. Pat. No. 4,659,641 discloses an improved process for the preparation of resin particles by bead polymerization, see the Abstract of the Disclosure for example; U.S. Pat. No. 4,816,366 discloses processes for the preparation of toners by certain suspension polymerization methods, see for example the Abstract of the Disclosure, and column 3; and U.S. Pat. Nos. 4,617,249; 4,849,316 and 4,971,879. The disclosures of each of the aforementioned patents are totally incorporated herein by reference.
In U.S. Pat. No. 4,507,378 there is illustrated a process for the preparation of toner compositions for electrophotography which involves polymerizing an aqueous suspension of a monomer such as styrene in the presence of a dispersant which includes a phosphate compound. According to the disclosure of this patent, once polymerization occurs the dispersant is removed by adding a dilute acid and a final product is obtained subsequent to rinsing with water. Furthermore, in U.S. Pat. No. 4,659,641, the disclosure of which is totally incorporated herein by reference, there is illustrated a polymerization process for toner resin compositions, reference Example I, wherein a styrene n-butyl methacrylate copolymer with 2 percent wax is dispersed in water. A suspending agent, such as tricalcium phosphate, and a surfactant in a monomer solution can be added to the initial mixture with a polymerization initiator such as benzoylperoxide. After polymerization occurs, nitric acid is added to remove the tricalcium phosphate and the final product is filtered, washed, and dried. In U.S. Pat. No. 4,894,309, the disclosure of which is totally incorporated herein by reference, there is illustrated a polymerization process for the preparation of crosslinked copolymers for toner resin compositions, reference Example I, wherein a styrene butadiene copolymer crosslinked with divinylbenzene is formed in an aqueous phase of tricalcium phosphate and an ALKANOL.TM.. After polymerization occurs, nitric acid is added to remove the tricalcium phosphate and the final product is filtered, washed, and dried.
Although the above-mentioned processes for preparing polymer particles may be suitable for their intended purposes in most instances, there remains a need for processes wherein there can be obtained polymer products of high purity, that is for example with no ash in the polymer resulting from the use of surfactant like tricalcium phosphate (TCP).
Bulk polymerization processes for the preparation of toner polymers are known. These processes involve charging monomers and initiator into a reactor vessel with no water as a heat transfer medium. The heat capacity of water is 1 whereas the heat capacity of monomers is 0.5. In bulk polymerization, the concentration of monomers is higher when compared to aquabulk or suspension polymerizations. Therefore, these processes are less effective in removing heat from the bulk polymerization by a factor of, for example, 2 as compared to the polymerization processes of the present invention wherein water is selected. Also, with these processes usually a lower temperature profile of around 50.degree. to 60.degree. C. is selected thereby requiring longer reaction times, for example twice as long as the processes of the present invention in embodiments to complete the polymerization.
The aforementioned and other disadvantages are avoided or minimized with the processes of the present invention. Other process advantages associated with the present invention include the avoidance of washing the resulting polymer with, for example, nitric acid for surfactant and stabilizer, such as TCP removal; no water rinsing is needed to remove the nitric acid and TCP solution from the polymer; solid/liquid polymer separation process like filtration can be avoided; drying of the polymer product is not needed; acid waste generation is avoided or minimized; and in the preparation of toner compositions, melt compounding of the molten polymer obtained with toner pigments/additives in the reactor on completion of polymerization eliminates the conventional extrusion blending.
Developer compositions with charge enhancing additives, which impart a positive charge to the toner resin, are known. Thus, for example, there is described in U.S. Pat. No. 3,893,935 the use of quaternary ammonium salts as charge control agents for electrostatic toner compositions, U.S. Pat. No. 4,221,856 which discloses electrophotographic toners containing resin compatible quaternary ammonium compounds in which at least two R radicals are hydrocarbons having from 8 to about 22 carbon atoms, and each other R is a hydrogen or hydrocarbon radical with from 1 to about 8 carbon atoms, and A is an anion; a similar teaching is presented in U.S. Pat. No. 4,312,933 which is a division of U.S. Pat. No. 4,291,111; and related teachings are presented in U.S. Pat. No. 4,291,112 wherein A is an anion including, for example, sulfate, sulfonate, nitrate, borate, chlorate, and the halogens.
Also, there is disclosed in U.S. Pat. No. 4,338,390, the disclosure of which is totally incorporated herein by reference, developer compositions containing as charge enhancing additives organic sulfate and sulfonates, which additives can impart a positive charge to the toner composition. Further, there are disclosed in U.s. Pat. No. 4,298,672, the disclosure of which is totally incorporated herein by reference, positively charged toner compositions with resin particles and pigment particles, and as charge enhancing additives alkyl pyridinium compounds. Additionally, other documents disclosing positively charged toner compositions with charge control additives include U.S. Pat. Nos. 3,944,493; 4,007,293; 4,079,014; 4,394,430, and 4,560,635 which illustrates a toner with a distearyl dimethyl ammonium methyl sulfate charge additive. The disclosures of each of the patents mentioned herein are totally incorporated herein by reference.
Moreover, toner compositions with negative charge enhancing additives are known, reference for example U.S. Pat. Nos. 4,411,974 and 4,206,064, the disclosures of which are totally incorporated herein by reference. The '974 patent discloses negatively charged toner compositions comprised of resin particles, pigment particles, and as a charge enhancing additive ortho-halo phenyl carboxylic acids. Similarly, there are disclosed in the '064 patent toner compositions with chromium, cobalt, and nickel complexes of salicylic acid as negative charge enhancing additives.
Toners with quaternary ammonium bisulfates are illustrated in U.S. Pat. No. 4,937,157, the disclosure of which is totally incorporated herein by reference, which bisulfates can be of the formula R'.sub.2 R".sub.2 N.sup.+ X.sup.- (R.sub.4 N)+X.sup.- wherein R' is aryl, substituted aryl such as alkylaryl, alkyl, preferably with 1 to about 30 carbon atoms, such as methyl, ethyl, propyl, butyl, hexyl, heptyl, and preferably dimethyl dialkyl ammonium bisulfate compounds where the dialkyl radicals are from about 10 to about 30 carbon atoms, and more preferably dialkyl radicals with from about 14 to about 22 carbon atoms; R" is aryl, substituted aryl such as alkylaryl, alkyl, preferably containing from 1 to about 18 carbon atoms; and X- is a bisulfate (HSO.sub.4) anion.